Multiplex telegraphy



'Jan. 4 1

927 H. A. AFFEL MULTIPLEX TELEGRAPHY Filed Dec. 15, 1924 ATTORNEY Patented 1...... 4.1927.

f UNITED STATES PATENT'OFFICE.

HERMAN a. arrnn, onmmwoob, NEW mnsnxlassrenon 'ro mm=ucm TELE- rnomr AND TELEGRAPH company, A conrom'rron or mew YORK.

HULTIPLEX TELEGRAPHY.

Application filed December 18, 1924. Serial No. 755,784.

Another object of my invention is to provide for receiving a carrier current message by the homodyne method and transmitting on the same frequency 90 degrees displaced from the received homodyne current, so that the transmitted message does not interfere with the received message. These and other objects of my invention will become apparent on consideration of an example which I have chosen for illustration in the accompanying drawings and which I now proceed to describe in the following specification. The invention willbe defined in the appended claims and itwill be understood that the following description relates to the particular embodiment here presented by way of example.

In the drawings, Figure 1 is a diagram I of the station at one end of a line operating according to my invention, andiFig. 2 is a diagramof the station at the other end of V such line.

At'the station WVest shown in Fig. 1, the constant speed motor M drives the alternating current generators G Gr and Gr of re; spective different frequencies These generators may be several armatures on the same shaft. The current from one of these generatorsGr goes to a' phase splitter comprising the resistance R and the condenser C in series. Accordingly, from the terminals of the resistance R and from the terminals of the condenser C, two currents may be drawn off 90 degress apart in phase. )ue of these currents is controlled by the sending key K which operates a reversing device S, chang- K.

trolled by the key'K passing over the con-' ductors 21 divides, part of it going to the filter F and the line, and part going over ing the phase 180; from this the current goes through the conductors 21 to the band filter F and thence through another filter F to the line L. The generator G, generates what may be called a pilot frequency current that goes through the band filter F and the filter F to the line L.

At the receiving station East shown in Fig. 2, the current of ilot frequency from the generator G goes t rough the filter F" "and the band filter F1, is amplified by the amplifier A and drives the synchronous motor SM. This motor SM drives the generators G and G,, at frequencies the same as for G and G respectively.

The current from the generator G goes through the adjustable phase shifter P and thence through a. phase splitter comprising the resistance R and condenser C the same as the phase splitter that has been described at the station West. The current component tapped from the terminals of the resistance R is controlled by the key K as described above for the key K and is .put'

through the band filter F and the filter F to the line L.

This signal current determined by the key K at station East passes over the line L and through the filters F and F and the branch conductors 22 to the primary -23 of a transformer. The design of the system is such and adjustments are made at the phase shifterP and the filters F and F which also act as phase shifters so that the received current in the transformer secondar1es24, 25 and 25, 26 are 90 degrees out of phase with the transmitted current controlled by the key K. 1

The current tapped from the terminals of the condenser G to the resistance R, is

also 90 degreesout of phase with the current controlled by the key K. The demodulators D and D operate on the principle employing homodyne current, which is obtained in this case from the terminals of the condenser C. F or effective demodulation the local homodyne current must be in phase with'the received current and that condition is satisfied in the present instance, both the received current and the homodyne current being 90 degrees displaced fromthe transmitted current controlled by the key Moreover, the transmitted current conand this product is of most substantial and marking and spacin effective value when the two currents are in phase and is ineffective when they are 90 degrees apart in phase.

Accordingly the received currents at station West determined by the operation of the key K at station East are not interfered with by the transmitted currents at station West which differ 90 degrees and are controlled by the he K.

The output circuit of the emodulator D, D includes the winding of the receiving polar relay X by means of which the received message may be interpreted in dots and dashes in the usual manner.

It will be noted thatthe diagram shows a balanced demodulator where the locally ap lied homodyne current supplies the same p0 arity to both grids. The current received from the distant end supplies positive potential to one grid at the instant that I it supplies negative potential to the other grid. Consequently, it is evident that when current is being received from the distant end, the effective magnetic flux in one winding will be increased,causing the polar relay armature to be moved to one side. When the transmitted current is reversed in phase, the relay flux is reversed, causing the armature to go to the opposite contact; It is evident, then, that reversing the phase of the transmitted current gives the efl'ect of signals.

If the key K 1s use to open the circuit between R and F instead of to reverse the phase, the signaling is accomplished by breaking the current, in which case a single tuhe demodulator can be used instead of 7 to another Winding of the input transformer, it will either double or neutralize the received current, making it possible to use a simple rectifier as a detector.

The box SR indicates sending and receiving apparatus similar to that which has been described in detail lying between the generator G and the filter F It will be seen that a plurality of duplex carrier current generators are provided, each based on a respective carrier current frequenc At the station East shown in ig. 2, the remaining apparatus not heretofore described in detail. is the same as that at station West. t

I claim:

1. The method of multiplex signaling, which consists in transmitting one way on a carrier current of a certain frequency, and transmitting the opposite way on a carrier current 0 the same frequency 90 degrees different in phase.

2. The method of multiplex signaling, which consists in transmitting one way on a carrier current 01 a certain frequency, and transmitting the opposite way on a carrier current of the same frequency, so as to receive at a phase difference of 90 degrees, and receiving by the homodyne method with locally generated current differing 90 degrees from the transmitting current, whereby the transmitting current is ineiiective on the receiver because of the phase difierence of 90 degrees.

3. A transmission line, meansto transmit from each end on the same carrier current frequency, so that the received currents Will be 90 degrees different in phase from. the transmitted currents at the same end, and means to distinguish the received currents and the transmitted currents by the phase difference.

4. Means to generate currents of the same frequency degrees apart, means to modulate one component for transmitting, means to receive a message in phase with the other" component, and means to apply said other component, to demodulate the received current.

In testimony whereof, I have signed my name to this specification this 12th day of December 1924.

V -HERMAN A. AFFEL. 

